two days ago, in regular update, IceWeasel converted into FirefoxESR 45.2.0
now, it will not resolve .onion addresses.
it is necessary to add Socks Proxy to FirefoxESR, to enable access to .onion domains? if yes, what socks proxy settings to use, to keep stream isolation from regular TorBrowser?
Iceweasel / Firefox will be stream isolated from Tor Browser anyhow, because Tor Browser uses SocksPort 9150. As long as you stay clear from that port, it will be stream isolated so or so.
FYI, you might get a message saying that you are not using Tor Browser. This is normal. (Documented?) Related to 2nd Tor Browser not connecting to Tor Control Port.